Power Tube Failure? Thin, Hum, etc...

[mcleanab]

Hey all!

New to this forum, so thanks in advance for any and all information!

My little fire breather Mark V:25 was kicking ***... swapped out some preamp tubes (was loaded with JJ's and the stock 'computer matched' Mesa power tubes), and sounded great. Then I noticed it got a tad fizzy and the low end was fading off... flipped the 25 to 10 watt switch and a very present hum kicked in, on both channels. Made sure the power tubes were nice and snug (preamp tubes as well) and it lasted for a few minutes sounding glorious, then back to the thin, lack of bass, and hum on the 10 watt mode. I can try rolling through the preamp tubes to see if there's a bad one, but I was worried I might damage the amp if it is the power tubes. (I could yank the power tubes and stick them in a different amp to see, I guess)...

Just turned it off and ordered new power tubes (Mesa matched).

Any thoughts or similar experiences? Looking for some guidance and assistance!

Thanks!

 

[tbonesullivan]

How long have you had the amp and how old is it? This could be a single tube, dirty contacts on a tube, or something else entirely.

 

[mcleanab]

How long have you had the amp and how old is it? This could be a single tube, dirty contacts on a tube, or something else entirely.

Got it in a trade about 2 years ago. All Mesa tubes. Replaced the preamp tubes with JJ's about a year ago. It's been great until the other day...

I did swap out the preamp tubes with some other ones, but now that this issue has started, doesn't matter what preamp tubes are in it...

 

[JustPassingThrough]

How old is the amp? The symptoms you're describing sound like those attributed to a filter cap failing, but they typically last 10+ years.